Conventionally, in order to respond to a demand for miniaturization and high-performance of high-frequency components (RF components) for use in mobile phones, developments of high frequency MEMS switches as high-frequency (RF) switches have been in progress by use of MEMS (Micro Electro Mechanical Systems) technology. The MEMS switches have, as features thereof, low loss, higher isolation, excellent distortion properties, and so on as compared with conventional semiconductor switches.
FIG. 29 is a cross sectional view illustrating a structure of a conventional MEMS switch 80j, and FIG. 30 is a plan view illustrating a functional portion KNj of the MEMS switch 80j. In FIG. 30, it should be noted that hatching is provided to non-cross sectional portions to clearly indicate a shape of each member.
In FIGS. 29 and 30, the MEMS switch 80j is formed of a substrate 81, a movable contact electrode 82 formed on the substrate 81, a stationary contact electrode 83, a movable driving electrode 84, a stationary driving electrode 85, a ground electrode 86, and so on. The movable contact electrode 82 and the movable driving electrode 84 are formed using an insulating material and integrally provided with a movable portion KB that constitutes a cantilever.
When a voltage is applied between the movable driving electrode 84 and the stationary driving electrode 85, electrostatic attraction is generated therebetween with which the movable driving electrode 84 is attracted and moved by the stationary driving electrode 85. In this way, the movable portion KB that is integrated with the movable driving electrode 84, and the movable contact electrode 82 move, and the movable contact electrode 82 touches the stationary contact electrode 83 so that the contacts close.
In FIG. 29, the functional portion KNj is turned upside down and housed in a package 87 made of ceramic which is filled with a nitrogen gas or the like, covered with a cap 88, and sealed. Each of the electrodes is provided with a bump BP and a terminal TB that utilizes a hole penetrating through the package 87. The MEMS switch 80j is mounted, for example, on an external printed board or the like using the terminal TB by soldering.
In this way, the functional portion KNj of the MEMS switch 80j is sealed by the package 87 and the cap 88 in a dry nitrogen atmosphere, which makes it possible to provide protection against breakage by an external force and secure stable opening and closing operation of the contacts.
A wafer level package structure is proposed as an example of a wafer level package (WLP). The structure includes a first substrate having functional elements and a second substrate that is bonded to seal each of the functional elements (Japanese Laid-open Patent Publication No. 2005-251898). According to the disclosure, the second substrate includes through holes that are arranged to face input and output electrodes, respectively, and first conductors filled into the through holes, whereby input and output terminals of each of the functional elements are arranged to include the through holes and the first conductors.
According to the conventional packaging method illustrated in FIG. 29, it is difficult to respond to a demand for miniaturization and a reduction in profile (low profile) because the package 87 made of ceramic which seals the functional portion KNj grows in size. It is also difficult to reduce the cost because the components of the package 87 made of ceramic and the sealing process require a fair amount of cost.
Such a device as the MEMS switch 80j having a movable portion requires a dicing process before the package 87 is sealed in the case where a wafer is used as the substrate 81 and a plurality of functional portions KNj are formed thereon. Accordingly, the movable portion may be damaged by a cutting fluid used for dicing or may be deformed by an action of surface tension of water during a drying process after the dicing process. To prevent this from being caused, conventionally, it is necessary to perform dicing with a sacrifice layer being left and chips after the dicing process are subjected to a process for removing the sacrifice layer, which leads to an increase in the number of processes and hence in cost.
In this respect, the packaging method proposed in Japanese Laid-open Patent Publication No. 2005-251898 does not cause such problems as damages and deformation of the movable portions in the dicing process because the dicing is performed while the first and second substrates are bonded together. However, since this method needs the second substrate that is thicker than the first substrate for sealing the functional elements provided on the first substrate, it still leaves a problem of reducing a profile (low profile) unsolved. In addition, an electrical loss in the penetration portion of wiring of the input and output terminals is not such a level to be ignored, and the issue of the cost still remains because the structures of the input and output terminals become complicated.